RennTech Performance Ecu Upgrade For Mercedes-Benz X166 GLS 550 Biturbo - AutoTalent }
RennTech Performance Ecu Upgrade For Mercedes-Benz GLS 550 Biturbo - AutoTalent }
RennTech Ecu Upgrade For Mercedes-Benz X166 GLS 550 Biturbo - AutoTalent }
RennTech Performance Ecu Tune For Mercedes-Benz X166 GLS 550 Biturbo - AutoTalent }
RennTech Performance Engine Upgrade For Mercedes-Benz X166 GLS 550 Biturbo - AutoTalent }
Description: RennTech HHT (hand held tuner) allows you the unlimited ability to switch between tuned and stock...
Vendor: RennTech
SKU: 54.166.GLS550BI
Product Type: Performance
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Subtotal: $2,240.00
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RennTech HHT (hand held tuner) allows you the unlimited ability to switch between tuned and stock ECU programming and requires no ECU removal. RennTech proprietary tuning module stores both the RennTech tuned file and your vehicles stock file. The module plugs directly into the OBD2 port and delivers the file you choose directly to the ECU. Programming takes only a few minutes and the vehicle can be reflashed at any time as many times as you wish.

RennTech intermediate level ECU upgrade for the Mercedes M278 engine still offers huge gains in performance across the entire RPM range, but with a slightly reduced peak HP and torque from our standard tune. This is ideal for customers who want increased performance in their daily driver without worry of extra strain on driveline components or for areas and countries with extreme altitudes, temperatures or fuel quality concerns.

RennTech intermediate ECU tune increases performance from 449 HP and 538 lb/ft torque up to 500 HP and 605 lb/ft at the crank! This is a slight reduction from our standard tune but still offers white knuckle performance at one of the most affordable price points in the tuning market.


We have found the M278 engine stock performance numbers vary from the baseline figures claimed by Mercedes Benz. We typically see higher baseline numbers than claimed by the factory.

Power gains are calculated based on stock numbers measured by RENNtech.

Crank Performance Numbers are calculated with a 18% Drivetrain loss on 4MATIC SUVs.

Our numbers will be dependent on conditions and fuel quality. 91+ Octane gasoline is mandatory with this Performance Upgrade.

States known for poor fuel quality have to be supplied with a lower power setup


  • Provides ability to switch between tuned and stock ECU programming
  • Providing comfort or daily driver reliability
  • Significant gains in horsepower
  • Increases the performance
  • Significant gains torque 
  • Gains: +26HP / +67LB-FT

Stock Performance:

  • 449 HP @ 5,500rpm; 516 LB-FT @ 2,000-4,500rpm
  • 474 HP @ 5,500rpm; 538 LB-FT @2,800-3,900rpm

Modified Performance:

  • 500 HP @ 5,500rpm; 605 LB-FT @ 3,700rpm
  • 410awhp @ 5,500rpm; 496awtq @ 3,700rpm

Vehicle Fitment:    

  • 2016 Mercedes-Benz X166 GLS 550 Biturbo
  • 2017 Mercedes-Benz X166 GLS 550 Biturbo
  • 2018 Mercedes-Benz X166 GLS 550 Biturbo
  • 2019 Mercedes-Benz X166 GLS 550 Biturbo
  • 2020 Mercedes-Benz X166 GLS 550 Biturbo


                            Images are for representation purpose only and may differ depending on application.

                              If you have any fitment questions, please feel free to reach out to our team via the contact methods below. If you are contacting us for any order status updates, please give us a call, or email us. We are a lean operation bringing you the best shopping experience possible. We are working on your orders as quickly as we can. We thank you for your patience.

                              Please reach out to us at (310) 231-0292 for sales inquiries if you are in the United States, Canada, Mexico.
                              For more in-depth product questions, fitment questions, product inquiries please email our performance specialists at
                              All other inquiries:
                              Please direct your inquiries to the chat functionality on our website.

                              Returns Policy

                              If a product is ordered and not wanted, the UNUSED item can be returned for a 25% restocking fee unless otherwise specified. In some cases, we may offer the ability to return the item to us for a lesser restocking fee and then keep the balance as a store credit. To return an item, it must be in brand new condition with original packaging.

                              We cannot accept a return on special ordered or custom items.

                              Shipping is non refundable in either direction unless approved by AutoTalent. All items wanting to be return MUST be reported within 30 days of the original invoice date. No items will be returnable after 30 days. All products shipped from the AutoTalent facility are shipped via FedEx, USPS, or USPS. Some packages shipped from the manufacturer may or may not require signatures for package release.

                              Special Order Items

                              Some items may be special order specifically for the customer’s vehicle. These items generally require a deposit or paid in full. Once this deposit amount is notified to the customer and they agree to order the special order item, the deposit becomes non-refundable. These special order items cannot be returned or resold. Cancellations are not allowed on special order parts.

                              AutoTalent DOES NOT REFUND SHIPPING CHARGES. If you modify, install, or alter the item in any form, we cannot accept it as a return. We will not cover any expenses related to the product or installation, and you may be required to purchase a replacement.

                              ** All cancellations that are requested that are NOT due to items not being in stock or delayed by the manufacturer are subject to a 5% processing fee. When you place an order with us we pay credit card fees that are NOT returned back to us. We will absorb these fees if we do not have the item in stock OR if you agree to the original ETA and that ETA is NOT met. If you decide to cancel for any other reason you will not receive this 5% fee back


                              We can ship to virtually any address in the world. Note that there are restrictions on some products, and some products cannot be shipped to international destinations.

                              When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.

                              Please also note that the shipping rates for many items we sell are weight-based.


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